PPC 113 is a compendium of fascinating articles, much admired by Bee Wilson, Gastropod, Regency Town House community project, Gastronomic History and Ken Albala. Here are a couple of recipes from the article by Reginald Smith on Malt Vinegar. Mother of vinegar, by the way is the liquid that forms on fermenting liquids, which turns into ascetic acid with the help of oxygen. When you add it to wine, apple, malt etc, it forms vinegar. For more information, you will need to read the full article!

RECIPES

Malt Vinegar

(using liquid or dry malt extract)

Dry or liquid malt extract

(type can be personal preference though barley-based ale

extracts approximate to traditional recipes)

Water

Brewing yeast (ale or lager)

Live mother of vinegar

Mix quantity of extract with water to adjust the specific gravity to a level that can ferment up to 6% potential alcohol by volume (roughly 1.05). For liquid yeast, pitch in directly. For dry yeast, soak in lukewarm water for 15 minutes and then pitch in. Keep in a warm place and allow alcoholic fermentation to proceed to completion (when bubbling stops and specific gravity is 1.0). Add mother of vinegar. The quantity should be one-fifth of the volume of the ale. Cover tightly with cheesecloth or another covering to allow air in but to prevent fruit flies from entering the fermenting vinegar. Place in a warm (25–30°C) place away from sunlight for two to four months. A thick mother should form on the surface and an increasingly acidic smell should develop over time. Testing with a pH meter can guarantee safety once pH is below 3.5 but acidity can only be measured by sodium hydroxide titration. The vinegar should be at least 4% acidity before use. Once the vinegar reaches 4.5% acidity, you can stop and it is important to measure acidity frequently after this point since allowing fermentation to continue for too long can cause bacteria to metabolize the vinegar and begin lowering its acidity. Make sure the vinegar reaches 5% acidity before using in canning.

Titration can often be done at a wine laboratory if you are unfamiliar with the process. Once the vinegar is made, put the mother (with enough vinegar to submerge it completely) in an airtight, twist-top container for preservation and future use. For the finished vinegar, you may bottle and use at will. If pasteurization is desired to prevent future fermentation, pasteurize it on a stove in a stainless steel pot at 65°C for 15 minutes.

Obtain milled malted grains and cook and sparge/mash as with regular wort preparation in order to reach a specific gravity of 1.06. Then follow the instructions after pitching the yeast in the previous recipe.